1. Field of the Invention
The present invention relates to a lighting controller of a lighting device for a vehicle and, more particularly, to a lighting controller of a lighting device for a vehicle that serves to control a lighting operation of a semiconductor light source constituted by a semiconductor light emitting device.
2. Related Art
Conventionally, there has been known a lighting device for a vehicle that uses, as a semiconductor light source, a semiconductor light emitting device, for example, a light emitting diode (LED). A lighting controller for controlling a lighting operation of the LED is mounted on the lighting device for a vehicle of this type.
Some lighting controllers include a single switching regulator, a plurality of current driving portions and a control portion (for example, see Patent Document 1).
The single switching regulator includes a transformer, a capacitor, a diode, an NMOS (Negative Channel Metal Oxide Semiconductor) transistor, and a control circuit. The single switching regulator functions as current supplying means for supplying a driving current to a plurality of LEDs.
A DC voltage input from an on-vehicle battery is converted into an AC voltage at a primary side of the transformer. The AC voltage, thus obtained, by the conversion is rectified by the diode and the current, thus rectified, is smoothed by the capacitor. The DC voltage, thus smoothed, is supplied to each of the LEDs.
Each current driving portion includes a comparison amplifier, an NMOS transistor, a PMOS (Positive Channel Metal Oxide Semiconductor) transistor, and a shunt resistor for detecting an LED driving current, and has a function for controlling ON/OFF operations and dimming of the LED through a constant current. Moreover, it is also possible to add a function for controlling ON/OFF operations to the current driving portion, thereby carrying out a control for changing a duty ratio of the ON/OFF operations.
[Patent Document 1] JP-A-2006-103477 Publication